Protective arrangement



June 25, 1929. R. E. CORDRAY 1,718,531

PROTECTIVE ARRANGEMENT Filed June 27, 1928 33/ E/ f'nventor z *5 vRichard Eflovdvm 1 7f by r m' Hi5 Attovneg.

Patented June 25, 1929.

UNITED STATES PATENT; OFFICE.

I RICHARD E. CORDR-AY, OF-SCHENEG'IADY, NEW YORK, ASSIGNOR- TO GENERALELEC- I T-RIC COMPANY, A CORPORATION OF NEW'YOR-K.

PROTECTIVE ARRANGEMENT.

Application filedJune 27,

of which any two of'at least threeare so arranged as to supply the rest.In differential protective arrangements, particularly such illas embodyauxiliarytransformers andv espeelally current transformers, differencesbetween characteristics of the transformers as actually manufacturedfrom an economical and practical standpoint, although unnecessaryto-consider for normal load conditions, becomegreatly exaggerated inaccordance with the severity of faults. Consequently, inv

case of through faultspthat is faults outside of the zone of protectiontobe considered, apparent differences may exist and effect erroneousoperation and therefore'interrupt the much desired continuityl-ofservice. Due to the rapid growth of the interconnection of powersystems; wherebyv large blocks of pow or are available to feed a fault,conditions'of ,this kind frequently appear, for example where thecircuits of two or more systems are connected to a transformer havingthree or more windings or where the circuits of three .or moresourcesare connected'to acommon bus. In such cases, any-source or anytwo or more sources may feed the rest so that the direction of power asregards input and outvput may vary greatly although neglecting lossesand assuming no fault conditions, the input and output are equal. .Ofcourse, if an attempt. is made to overcome the difficulty du'e to thelack' of balance-in the characteristics of the transformers aspractically construct.- ed, by giving higher vsettings to the faultresponsive apparatus such as relays-and the like, the sensitivity ofprotection is sacrificed. In some cases. the power transformer may beprovided with a. voltage regulating means which, when off thezeroposition, upsets the balance of the current transformers to the extentof thepercentage of-voltage regulation employed. This furtheraccentuates the difficulty of correlating sensitivity and continuity ofservice. An object ofmy invention is to provide for three or morecircuits of. which any two of at least three new arranged so as to beable to supply the rest, an improvedprotective arrangement whereby tobta n max mu sensitivity and vet avoid 192s. Serial No. 288,719.

erroneous operation on faults outside the protected zone. A furtherobject of my invention is to provide an improved protective arrangementin which the operation of the protective apparatus is based on apredetermined ratio of unbalance between corresponding electricalquantities of the three or more cir cuits to be protected and not on amere diiierence between" one of said quantities and a 1 function of theremainder. Other objects of my invention will appear hereinafter.

My invention willbe better understood from the following descriptionwhen considered'in connection with the accompanying drawing and itsscope will be pointed out in the appended claims. V

In the accompanying drawing, Fig. 1 illus trates partly in diagram andpartly in perspective, a protective arrangement for three inductivelyrelated circuits shown in single phase for clearness; 2 illustrates diagrammatically an arrangement similar to Fig. 1 for four inductivelyrelated circuits; and Fig. 3 illustrates diagrai-nn'iatically anarrangement similar to Fig.- 1 for 'three'conductively related circuits.

In the'embodimentof my invention shown inrFig'. 1, a plurality .ofcircuits 4, 5, 6 are inductively related, as shown, by being connect-edrespectively to the mutually inductive windings 7, 8,-9 of a powertransformer 10. Thismaybe arranged for voltage regulation. schematicallyindicated by the adj ustable lead to the windingff. Each of the circuits1, 5,

its stored energy tothe fault. In any event,

it possible for any one of the circuits 4, 5, 6 to supply the others,any two to supply the third or all three to supply a fault within thetransformer f. Obviously, the relative directions of power may varygreatly even during normal conditions and also on through faults, thatis those occurring outside of the transformer or the Zone to beprotected between the circuit breakers. However, .un-

- of the circuit currents.

der normal conditions as Well as on through faults, the power fed to thetransformer 10 is, neglecting losses, equal to the power takentherefrom. This balance is disturbed on the occurrence of a fault withinthe transformer.

In order to obtain maximum sensitivity and yet prevent unnecessaryinterruptions ofscrvice, I provide in accordance with my invention meansfor controlling one or more of the circuits 4, 5, 6 through an operatingeffect which is dependenton the' difference between the input and outputcurrents of the circuits and cumulative restraining effects dependent onthe circuit currents butiindependent of the relative directions ofpower,

' type. As shown, this circuit includes current transformers 20, 21, 22respectively associated with the circuits 4, 5, 6; The restrainingwindings 17, 18, 19 are connected in series with the currenttransformers 20, 21, 22 respectively and to a common point 23 betweenwhich and another point, 24 normally at the same potential, theoperatingwinding 16 is connected. In order to use standard current transformersand yet allow for the turn ratios of the power transformer 10 and thevoltage regulation thereof suitable means such as one or more adjustableauto-transformers 25, 26 may be provided. lVit-h this arrangement eachof the restraining windings 17, 18, 19 will be energized by acurrentproportional to the current in the circuit with which its respectivecurrent transformer is associated and the operating winding 16 will beenergized by a current dependent. on the difference between the inputand outputcurrents of the circuits 4, 5,6.

The relay 15 may be of the induction disk type and as illustratedincludes a movable member such as'the contact controlling arm 27 securedto a shaft 28 on which are mounted one or more disks 29, 30 of electriccurrent conducting material.

these windings may be respectively applied to shaded-pole-motor elements31, 32, 33, 34

inductively associated with the disks 29, 30,

- two disks-being preferably employedin order to avoid the possibilityof magnetic intei--' ference between the elements. The three re- .diskis dependent only on the positioning of the short-circuited or shadingwinding, the directions of the torques exerted by the motor elements 31,32, 33, 34 are independent of the directions of the currents in thewindings 16, 17, 18 and 19 and, therefore, of the relative directions ofpower in the circuits 4, 5, e.

The expression for the resultant. torque,

for moving the circuit controlling arm 27 is 1 where 1,, I I representthe currents in the respective circuits, nbeing the number of circuits Iand I represent the sum of the currents supplied by andtaken from thecircuits 4,5,. and 6. .fVhere a plurality of circuit breakers 11, 12, 13are to be controlled it is-preferable in order to avoid severe dutyonthe contacts of the sensitive protective relay 15 to have it controlan intermediate or auxiliary device such as a relay 37 which is arrangedto control the circuits of the trip coils-14. In accordance with myinvention I preferably base the operation of the relay 15 not on themere difference between the effect on the operating winding 16 and thecombined cumulative effects of the restraining windings 17, 18, 1'9 buton a predeter- *llllllt .1 ratio between these effects. This may de doneby suitably proportioning the turns of the operating winding 16 to-theturns of ,the restraining windings 17, 18,19 so that tripping iseffected only'when the ratio between the effcctsexerted by the operatingand restraining windings exceeds a predeter-- mined value. Then onthrough faults which cause heavy currents, the same relay balance ismaintained and even -though current transformer characteristics may varyconsiderably, the relay 15 can be set to maintain itself ineffective totrip until a fault occurs in the zone which itis intended to protect. Infact this ratio balance action may be such as to permit considerablevariation in the voltage of the power transformer 10 when a voltageregulating unit .is associated therewith.

Assuming a through fault on the circuit 5,

of the circuits 4 and 6 will feed the fault but the input and outputcurrents of the circuits remain substantially equal so that the points23 and 24: should be at the same potential.

that is beyond thecircuit breaker 12, then both Under these conditionsnocurrent appears in the operating winding 16. Therestra1n1ng windings17, 18,19 will be energized by carrents proportional to those appearinginthe'.

case of severe through faults due tounbal ence in current transformercharacteristics. This apparent (liiierence, however, is 1nsut' ticientto overcome the restra nt due to the efcase no matter what two-circuitsfeed'a faulty circuit or whether one circuit happens to feed twocircuits simultaneously at fault; In case of internal faults on thepower transformer all of the circuits 4, 5 and 6 may feed the fault.Here again the restraint is dependent on the sum of the eiiects on thewindings 17, 18, 19. Under these conditions, however, the

. inputand output currents of the transformer 10 are not balancedand thepoints 23 and :24 difi'er more or less in potential dependent on theseverity of the fault. .T he difference between the input and outputcurrents now becomes equal to the sum of the circuit currents. Thisappears in the operating winding 16 whence it is divided among therestrainin r windings 17, 18.19 but because of the preponderance ofturns in the operating wind the operating-effectexceeds the restrainlngeit'ect. Consequently therelay15 closes the circuit of the auxiliary'relay 37 and thereby eflects'the operation of the circuit breakers 11,12 and 13. i

In the embodiment of my inyention shown in Fig. 2 four inductivelyrelated circuits 4,

I 5, 6 and 38 are shown coupledthrough the power transformer 10' havingwindings 7, 8,- 9 and S9. IVith this arrangement assuming that thecircuit 38 may also supply power, the protective relay 15 which isschematicall illustrated, is provided with an additional restrainingwinding elO connected-to be energized in accordance with the current inthe circuit 38 through a current transformer 41 and a suitableauto'transt'ormer 42. The

, operation of this modification of my invention will be obvious onreference to the description of Fig. 1 as it is merely an extension ofthe arrangement shown in Fig. 1 to four circuits instead of three. Ifthecircuit '38 is not connected to a source or to anymeans which couldsupply current even temporarily, it is unnecessary to supply the extrawinding 40, the restraining effect due to the current of the circuit 38being obtained by arranging for one of the restraining windings 17, 18,19 to be energized by this current In the embodiment of my inventionshown in Fig. 3 the circuits 4, 5 and 6 are conductively related and mayform for example the the arrangement showninFig. 1 and operates in thesame manner. k p lVhile I have shown and describedmy invention inconsiderable detail Ido not desire to be limited tothe exactarrangements shown,

-but seek to cover in the appended claims all feet of therestrainingwindings'li, 18. and 19. This, it will be apparent, is always the thosemodifications that fall within the true spirit and scope ofmy invention.

hat Iclaim as new and desire to secure by'Letters Patent of theUnitedStates, is -1. In combination, three or more electric circuits of whichany two of at least three are arranged to supply the rest, and means forcontrolling said circuits including a relay having a movable member, an.operating winding connected to beenergized in accordance with thedifference between the input ent on only hthe magnitudes of the circuitcurrents. I

3. In combination, three or more electric circuits of which any two ofat leastthree are arranged to supply the rest, and means for controllingone of said circuits including an ,electroresponsivedevice having meansconnected and arranged to produce an effect dependent on the ditl'erencebetween the input and output currents of said circuits and a pluralityof opposing means respectively connected to be energized in accordancewith the circuit currents and arranged to'act cumulatively independentlyof the relative directions of the currents.

4. In combination. three electric circuits of which any two are arrangedto supply the rest, and means for controlling one of said cireuitsriiicluding a relay having a movable member and operating means thereforin cluding torque exerting means connected and arranged to exert atorque dependent on the difference between the input and output currentsof the circuits and an opposing torque exerting means for each circuitconnected to be energized in accordance with the current of theassociated circuit, said elements being arranged to exert cumulativetorques on said member dependent on only the magnitudes of the currents.

' 5. Incombination, a power transformer having three or more mutuallyinductively related windings of which any two of at least three arearranged to supply the rest, and means for controlling the circuit ofone ofsaid windings including a relay having a movable member, means foroperating saidmember arranged to be energized in accordance withthcdifference between the input and output currents of said windings andmeans associated with each winding and arranged to exert on said membercumulative restraints dependent on only the magnitudes of the currentsin the respective windings.

6. In combination, three or more electric circuits of which any two ofat least three are arranged to supply the rest, means for controllingone of said circuits, including an electroresponsive device connectedand .arranged to be controlled in accordance wlth 'the differencebetween two effects respective ly dependent on (If-l-[fi- +13) and,

(I ,I where 1 ,1 In represent the currents in the respective circuits, nbeing the number of circuits I and I represent respectivelythe sums ofthe currents supplied by and taken from said circuits.

7. In combination, three or more inductively related circuits of whichany two of at least three are arranged to supply the rest,

ditlerentiaLrelaymeans for controlling said circuits'including anoperating winding con nected to be'energized in accordance with thedifference between the input and output cur- I rents of the circuits, aplurality of restraining windings respectively connected to be energizedin accordance with thecircuit currents and arranged to exert cumulativeeffects dependent on only the magnitudes of the currents,andinterruptin'gmeans in one of said "circuits arranged to be actuated inresponse to the operation of said relay when the ratio between theeffects exerted by the operating and restraining windings'exceeds apredetermined value.

8. In combination, three or more electric circuits ofwhich any two of atleast three are arranged to supply the rest-{means for controlling saidcircuits including an electroresponsive device subject to an operatingef feet dependent on the difierence between the input and outputcurrents of said circuits and rents, and circuit interrupting means inone of sa dcircuits arranged to-beioperated when the ratio between theoperating and the 're-Y straining effects exceeds a' predeterminedvalue;

9. In combination, three or more electric power circuits of which anytwo of at'least three"are arranged to supplylth'e rest, and means forcontrolling one of saidcircuits ineluding a relay having an operatingwinding and 'a plurality of restraining windings and a circulatingcurrent protective circuit including. said restraining wlndingsrespectively connected in series relationjwith said power circuits andto a common point, said operating win'ding being connected between saidcommon point and a point in said protective circuit normally at the samepotential.

In witness whereof, I have hereunto set my hand this 26th day of June,1928.

RICHARD E. CORDRAY,

to cumulative restraining effects dependent on only the magnitudes ofthe circuit cur-

